P855: FERROPTOSIS AS A NEW BCMA-TARGETED IMMUNOTHERAPY OFF-TARGET EFFECT IN MULTIPLE MYELOMA
Authors: Enrico La Spina, Alessandra Romano, Daniele Tibullo, Cesarina Giallongo, Grazia Scandura, Daniela Cambria, Sebastiano Giallongo, Palumbo Giuseppe Alberto
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: Triple-class or penta-drug refractory Multiple Myeloma (MM) patients develop multi-drug-resistant disease with poor survival. BCMA is a transmembrane receptor, homogeneously and highly expressed on the surface of MM-plasmacells (MM-PCs). While Belantamab-Mafodotin (BeMa), was the first mAbs approved, new generation drugs are of particular interest because of their ability to redirect T cells to MM-PCs. Elranatamab (ELra) is a BsAbs that target simultaneously BCMA and CD3 leading to the formation of immunologic synapses with subsequent tumor PCs lysis. Although, BeMa and T cell redirecting BsAbs, are showing promising results, drug resistance (DR) mechanisms are highly frequent. Several studies demonstrated that in cancer cells, excessive lipids are stored in lipid droplets (LDs), which represent a source of precursors for the formation of various lipids as, mono, and polyunsaturated fatty acids (MUFA and PUFA). An increase in MUFA, through SCD1, markedly alters signal transduction, protects cancer cells from oxidative damage such as lipid peroxidation potentially leading to DR. In tumor microenvironment cells dying also by ferroptosis, due to an overproduction of lipid peroxides (LOOH) by ferroptotic cells, because of weak antioxidant system with downregulated glutathione peroxidases 4 (GPX4). Herein, we demonstrate a DR mechanism adopted by Human MM cell lines (HMCLs) when co-cultured with CD3 and/or CD8 T cells. Aims: Since our research group demonstrated that, BeMa exposure induce ferroptosis, in sensitive cytotype (U266-S) compared to the resistant one (OPM2-R) (in submission), thus, the first aim was to demonstrate whether ELra treatment may favour the onset of DR in OPM2-R co-cultured with purified CD3 and/or CD8 T cells at different effector-to-target (E:T) cell ratios. The second aim was to measure cytoplasmatic LDs amount in HMCLs prior ELra treatment together with lipidomic and transcriptomic analysis, to predict the intrinsic vulnerability of HMCLs to ferroptosis and to identify differential expression and pathways activation. Methods: Combining in vitro and ex vivo assays, FACS, qRT-PCR, RNA-seq it was evaluated the response to ELra treatment in co-cultured T cell-HMCLs. Results: Despite no significant differences in BCMA surface expression levels, sensitivity to ELra was largely variable. In vitro, unstimulated CD3 and/or CD8 cells co-cultured with several HMCLs and increasing concentrations of ELra, induced dose-dependent redirected lysis of PCs after with EC50 values ranging from 25 to 100 ng/mL. Cell viability of OPM2-R was not affected compared to U266-S confirming both the establishment of a resistant cytotype and the specificity of ELra for BCMA, in E:T ratio independent-manner. To confirm ELra-mediated ferroptosis, lipid peroxides formation after drug exposure was found significantly increased with a LDs decrease in U266-S compared to OPM2-R. Due to LOOH increase in U266-S, ferroptosis hallmarks GPX4 and SLC7A11 resulted downregulated while the pro-ferroptotic ACSL4 was significantly increased confirming a ferroptosis-primed sensitive phenotype. While PUFA oxidation is pro-ferroptotic, MUFA formation promotes ferroptosis-resistant cell state. In accordance, lipidomics analysis demonstrated higher MUFA/PUFA ratio in OPM2-R and increased expression levels of SCD1. Summary/Conclusion: This study corroborated a previously described ferroptosis as new off-target effect of anti-BCMA therapy, independent on BCMA expression but favoured by a balanced MUFA/PUFA ratio and a roboust antioxidant system, to reopen a new therapeutic scenario for anti-BCMA therapy in MM. Keywords: Multiple myeloma, Lipid metabolism, Multidrug resistance, Immunotherapy